2-Acrylamido-2-methylpropanesulfonic acid and analogues thereof, mainly as a co-monomer and homo-monomer, are widely used in many industries. This kind of compounds is a strong acidic substance. Before use, it is usually neutralized with an alkaline substance to prepare a salt solution of pH7-10, for example. This neutralization process has certain technical difficulty, since it is necessary to avoid problems, such as, unwanted yellowness of the solution, increased viscosity, and even a large scale of self-polymerization. Therefore, some users (factories) do not purchase acidic solid itself of such compounds, but purchase the aqueous solution of salt generated after neutralization from a manufacturer, the weight percent concentration thereof being usually 50%˜58%. This aqueous solution, as a commodity in transaction, has some unfavorable factors, such as higher cost of intercontinental ocean transportation, but only about half of it is the effective substance really needed, and the rest of the transportation is just water. For high concentration of polymeric monomer solution, it is necessary to make as short as possible the storage time in a factory for manufacturing or using it and the transportation time for transporting it between two places, so as to avoid the possible increase in viscosity or even a large scale of polymerization. Moreover, there are some special requirements for transport and storage conditions, such as avoiding direct sunlight, requiring ventilation to avoid too high temperature and so on. In addition, the product of aqueous solution is not suitable for uses in some non-aqueous systems, and the solution, the highest concentration of which is 50˜58%, is also not suitable for usages demanding a higher concentration.
In literature and production practice, re-crystallization and purification of 2-acrylamido-2-methylpropanesulfonic acid solid itself are introduced widely, but a final product of these refining processes is acidic solid itself of 2-acrylamido-2-methylpropanesulfonic acid, rather than derivative salts after the neutralization reaction thereof. U.S. Pat. No. 6,331,647B1 describes a method for preparing solid of derivative salt obtained through a neutralization reaction of such compounds for the purpose of purification. The method comprises: making this kind of acidic compounds completely react with a alkaline substance in water at pH of 7 to 12.5 at −20° C.˜75° C.; removing any solids by filtration; and performing re-crystallization on the solution, so as to obtain again a solid which is purified but present in a form of a salt. The re-crystallization is achieved by increasing the temperature and/or performing concentration through removing water and reducing pressure, or reducing the solubility of targets by decreasing the temperature. This method requires that the substance to be purified is completely dissolved in water, therefore during the later process for obtaining a solid again by re-crystallization, it is necessary to consume a lot of energy if the concentration through removing water is applied; and the effect is limited and a large amount of targets would also be dissolved in water if the approach of decreasing the temperature is applied. Thus, this method is more difficult to be commercialized in terms of cost and efficiency, and currently this kind of industrialization salts in a solid form has not appeared in the market.